Despite progress in solid-state battery engineering, our understanding of the chemo-mechanical phenomena that govern electrochemical behaviour and stability at solid-solid interfaces remains limited ...compared to at solid-liquid interfaces. Here, we use operando synchrotron X-ray computed microtomography to investigate the evolution of lithium/solid-state electrolyte interfaces during battery cycling, revealing how the complex interplay among void formation, interphase growth and volumetric changes determines cell behaviour. Void formation during lithium stripping is directly visualized in symmetric cells, and the loss of contact that drives current constriction at the interface between lithium and the solid-state electrolyte (Li
SnP
S
) is quantified and found to be the primary cause of cell failure. The interphase is found to be redox-active upon charge, and global volume changes occur owing to partial molar volume mismatches at either electrode. These results provide insight into how chemo-mechanical phenomena can affect cell performance, thus facilitating the development of solid-state batteries.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
A stable anode‐free all‐solid‐state battery (AF‐ASSB) with sulfide‐based solid‐electrolyte (SE) (argyrodite Li6PS5Cl) is achieved by tuning wetting of lithium metal on “empty” copper ...current‐collector. Lithiophilic 1 µm Li2Te is synthesized by exposing the collector to tellurium vapor, followed by in situ Li activation during the first charge. The Li2Te significantly reduces the electrodeposition/electrodissolution overpotentials and improves Coulombic efficiency (CE). During continuous electrodeposition experiments using half‐cells (1 mA cm−2), the accumulated thickness of electrodeposited Li on Li2Te–Cu is more than 70 µm, which is the thickness of the Li foil counter‐electrode. Full AF‐ASSB with NMC811 cathode delivers an initial CE of 83% at 0.2C, with a cycling CE above 99%. Cryogenic focused ion beam (Cryo‐FIB) sectioning demonstrates uniform electrodeposited metal microstructure, with no signs of voids or dendrites at the collector‐SE interface. Electrodissolution is uniform and complete, with Li2Te remaining structurally stable and adherent. By contrast, an unmodified Cu current‐collector promotes inhomogeneous Li electrodeposition/electrodissolution, electrochemically inactive “dead metal,” dendrites that extend into SE, and thick non‐uniform solid electrolyte interphase (SEI) interspersed with pores. Density functional theory (DFT) and mesoscale calculations provide complementary insight regarding nucleation‐growth behavior. Unlike conventional liquid‐electrolyte metal batteries, the role of current collector/support lithiophilicity has not been explored for emerging AF‐ASSBs.
Lithiophilic Li2Te is synthesized by exposing the collector to tellurium vapor, followed by in situ Li activation. The Li2Te significantly reduces the electrodeposition/electrodissolution overpotentials and improves Coulombic efficiency. An anode‐free all‐solid‐state battery employing a sulfide‐based solid‐electrolyte (argyrodite Li6PS5Cl) with NMC811 cathode delivers an initial CE of 83% at 0.2C, with a cycling CE above 99%.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Metal anode-based battery systems have been deemed indispensable towards energy storage renaissance engendering extensive research into strategies countering dendritic growth of metal ...electrodeposition. Fundamentally, the morphological evolution of a material is uniquely characterized by the heights of its self-diffusion barrier across multiple pathways. Herein, based on a coarse-grained kinetic Monte Carlo method, we derive insights into the nucleation and growth of metallic electrodeposits in liquid electrolytes, governed by surface self-diffusion characteristics cognizant of the diverse diffusion routes including terrace, away from step and interlayer pathways. We deconvolve the roles played by each of these surface diffusion mechanisms in conjunction with the electrochemical reaction rate on the deposition morphology regime (film
vs.
mossy
vs.
fractal). We identify interlayer diffusion as the predominant morphology-determining mechanism; dendrite-free deposition even at moderate current rates constrains this diffusion barrier to an upper limit. Additionally, we highlight subtle features amidst the realm of the morphological growth assortment that connect to the cell's electrochemical performance. Finally, we delineate morphological features of Li, Na, Mg and Al based on their respective surface diffusion barriers and applied overpotentials, and provide a baseline for the interpretation of experimental observations. This fundamental study sheds light on the mesoscale underpinnings of morphological variances in mono-valent and multi-valent metal electrodeposition.
Transformation of the electrodeposition morphology, facilitated by the surface self-diffusion across a step
Solid‐state batteries (SSBs), utilizing a lithium metal anode, promise to deliver enhanced energy and power densities compared to conventional lithium‐ion batteries. Penetration of lithium filaments ...through the solid‐state electrolytes (SSEs) during electrodeposition poses major constraints on the safety and rate performance of SSBs. While microstructural attributes, especially grain boundaries (GBs) within the SSEs are considered preferential metal propagation pathways, the underlying mechanisms are not fully understood yet. Here, a comprehensive insight is presented into the mechanistic interactions at the mesoscale including the electrochemical‐mechanical response of the GB‐electrode junction and competing ion transport dynamics in the SSE. Depending on the GB transport characteristics, a highly non‐uniform electrodeposition morphology consisting of either cavities or protrusions at the GB‐electrode interface is identified. Mechanical stability analysis reveals localized strain ramps in the GB regions that can lead to brittle fracture of the SSE. For ionically less conductive GBs compared to the grains, a crack formation and void filling mechanism, triggered by the heterogeneous nature of electrochemical‐mechanical interactions is delineated at the GB‐electrode junction. Concurrently, in situ X‐ray tomography of pristine and failed Li7La3Zr2O12 (LLZO) SSE samples confirm the presence of filamentous lithium penetration and validity of the proposed mesoscale failure mechanisms.
The morphological stability of lithium metal electrodes in solid‐state batteries remains a major challenge. In this work, the electrochemical‐mechanical interactions and competing ion transport dynamics underlying the stability of grain boundary‐electrode junctions is examined. A mechanistic failure pathway including cavity growth and strain hotspot evolution is triggered due to the ionic transport mismatch between the grains and grain boundaries.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The solid electrolyte interphase (SEI) plays a pivotal role in enabling fast ionic transport and preserving the battery electrodes from parasitic reactions with solvents. However, due to large volume ...changes of lithium (Li) electrodes, the SEI layer can potentially undergo mechanical failure, resulting in electrolyte degradation. The mechanical stability of the SEI is a critical aspect that needs to be modulated for designing rechargeable metal batteries with optimal performance. In this work, we perform density functional theory calculations to investigate the mechanical properties of lithium fluoride (LiF) and lithium oxide (Li2O) nanofilms and quantify the Li surface diffusion kinetics over these two SEI materials. Based on our analysis, it is identified that Young’s modulus and the ideal strength of the SEI are strong functions of the nanofilm thickness and crystallographic direction. Interestingly, we find that mechanical strain substantially alters the Li surface diffusion behavior on the SEI. For a strain of 4%, while the Li surface diffusion rate decreases by two orders of magnitude on the stretched Li2O film, it increases two times on the stretched LiF film, indicating critical implications on the morphological stability of the metal anode. A fundamental correlation between inherent SEI properties and Li plating behavior is revealed, suggesting a potential pathway to achieve dendrite-free electrodeposition via SEI modulation.
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IJS, KILJ, NUK, PNG, UL, UM
Dendrite formation and growth upon cycling pose major concerns toward lithium metal battery performance and safety. Herein, we present an interface-capturing formalism to study the morphological ...evolution of lithium metal anodes at time scales comparable to typical charging durations. This mesoscale study distinctly captures mossy/fractal growth patterns that manifest depending on the electrochemical environment of the lithium metal battery system and observed in in situ experimental electrodeposition studies. We further develop a safety map (pertaining to the short circuit via direct dendrite propagation) in terms of charged capacity and the limiting current density of the system. Examination of the safety map, in conjunction with the delineated morphological features (growth speed and interfacial area, in particular), allows deriving insights into probable cell failure modes. We deduce that the electrolyte starvation and solid electrolyte interphase reformation are more likely causes for cell failure, that are instigated at higher applied current densities than direct dendrite penetration itself.
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IJS, KILJ, NUK, PNG, UL, UM
Solid-state batteries (SSBs) hold the potential to enhance the energy density, power density, and safety of conventional lithium-ion batteries. The theoretical promise of SSBs is predicated on the ...mechanistic design and comprehensive analysis of various solid–solid interfaces and microstructural features within the system. The spatial arrangement and composition of constituent phases (e.g., active material, solid electrolyte, binder) in the solid-state cathode dictate critical characteristics such as solid–solid point contacts or singularities within the microstructure and percolation pathways for ionic/electronic transport. In this work, we present a comprehensive mesoscale discourse to interrogate the underlying microstructure-coupled kinetic-transport interplay and concomitant modes of resistances that evolve during electrochemical operation of SSBs. Based on a hierarchical physics-based analysis, the mechanistic implications of solid–solid point contact distribution and intrinsic transport pathways on the kinetic heterogeneity is established. Toward designing high-energy-density SSB systems, the fundamental correlation between active material loading, electrode thickness and electrochemical response has been delineated. We examine the paradigm of carbon-binder free cathodes and identify design criteria that can facilitate enhanced performance with such electrode configurations. A mechanistic design map highlighting the dichotomy in kinetic and ionic/electronic transport limitations that manifest at various SSB cathode microstructural regimes is established.
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IJS, KILJ, NUK, PNG, UL, UM
Large volumetric changes and dendrite growth are major challenges to achieving enhanced cycling efficiency and safety in lithium (Li) metal batteries. Porous hosts for Li storage can potentially ...accommodate large volumetric changes and enable stable deposition morphologies. In this study, we mechanistically explore the Li electrodeposition process in porous host architectures that contain well-aligned channels. It is identified that the channel architecture helps regulate Li-ion flux and stabilize Li electrodeposition when the channel size is comparable to the characteristic size of the dendrites. Dendrite growth due to local inhomogeneity in ion flux/reaction kinetics can be alleviated through the confinement effect of vertically aligned channel walls. The critical effect of host architectural features, such as channel patterns, pore size, and connectivity, on the local morphological stability have been quantified. For high-rate applications, vertically aligned channel design with minimal interchannel connectivity is found to be an effective strategy for dendrite suppression when compared to horizontally aligned channels. This study provides fundamental insight into Li morphological growth within porous host architectures, identifying design guidelines to address the interfacial instability challenges in Li metal batteries.
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IJS, KILJ, NUK, PNG, UL, UM
Aluminum oxide (Al2O3) nanopowder is spin-coated onto both sides of commercial polypropene separator to create artificial solid-electrolyte interphase (SEI) and artificial cathode electrolyte ...interface (CEI) in potassium metal batteries (KMBs). This significantly enhances the stability, including of KMBs with Prussian Blue (PB) cathodes. For example, symmetric cells are stable after 1,000 cycles at 0.5 mA/cm2 - 0.5 mAh/cm2 and 3.0 mA/cm2 - 0.5 mAh/cm2. Alumina modified separators promote electrolyte wetting and increase ionic conductivity (0.59 vs. 0.2 mS/cm) and transference number (0.81 vs. 0.23). Cryo-stage focused ion beam (cryo-FIB) analysis of cycled modified anode demonstrates dense and planar electrodeposits, versus unmodified baseline consisting of metal filaments (dendrites) interspersed with pores and SEI. Alumina-modified CEI also suppresses elemental Fe crossover and reduces cathode cracking. Mesoscale modeling of metal - SEI interactions captures crucial role of intrinsic heterogeneities, illustrating how artificial SEI affects reaction current distribution, conductivity and morphological stability.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Solid-state batteries, because of their high energy density, are promising candidates for long-range electric vehicles and electric aviation. While the enhanced safety potential of solid-state ...batteries has been typically ascribed to the nonflammability of solid electrolytes, an extensive interrogation of their thermal stability is still required. In this work, we reveal how the thermal stability in sulfide-based solid-state batteries is critically dependent on the interphase interactions at the solid electrolyte/Li interface, thereby illustrating the drastically different thermal signature of Li10SnP2S12 when compared with Li3PS4 and Li6PS5Cl. Our study shows that thermal runaway occurs even for a pristine Li10SnP2S12/Li interface and is severely exacerbated with cycling, which exhibits a massive thermal spike at the melting point of Li; this shift in thermal response uniquely correlates to the Li10SnP2S12 interphase evolution. On the basis of these distinct thermal signatures, cell-level mechanistic safety maps cognizant of the Li/interphase interaction, cathode/Li crosstalk, and specific energy are delineated.
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IJS, KILJ, NUK, PNG, UL, UM
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